The starter battery of a motor vehicle is an accumulator that provides at least the electrical current for the starter of a combustion engine. The battery of an electric vehicle that is used to drive the vehicle is, in contrast, referred to as the traction battery. Furthermore, electric vehicles or hybrid vehicles can also comprise a starter battery. Lead accumulators by way of example can be used as batteries and said lead accumulators are also described herein as lead acid batteries.
Starter batteries are typically charged during the journey by a generator, such as an alternator. The operating state of the vehicle can be used as an aid for the charging strategy to increase the serviceable life of the starter battery. As an example, U.S. Pat. No. 4,937,528 provides in one embodiment that a generator is switched on and off depending upon the charge state of the battery and the operating state of the vehicle. The generator can be switched off if the charge state of the battery has achieved a defined value and has not yet dropped back to below a lower threshold value. However, if the vehicle is in a situation in which the current requirement is increased, it is possible to provide that the generator remains switched on even if the charge state of the battery has already returned to a defined threshold value. These situations can occur by way of example at night, in winter, or if the air-conditioning is running.
A plug-in hybrid vehicle or electric vehicle is normally charged at the power grid until the traction battery has been fully charged. The charging system of the vehicle is subsequently automatically deactivated. However, in the event that a low charge state of the starter battery is detected, the strategy can be extended to also charge the starter battery at the power grid. The charging system of the vehicle is then not switched off after the traction battery has been fully charged, but rather continues with equalizing the charge of the starter battery.
Fundamentally, the starter battery must be sufficiently charged so that the vehicle can be started at the next opportunity and the low voltage current supply of the vehicle (12V) can be supplied with a minimum voltage level during the transient periods of high current. However, it can take a whole day to fully recharge a battery and a long charging period of this type can cause customer dissatisfaction. The reason for this is, on the one hand, the current costs, but also the unusual behavior of the vehicle owing to the fact that it is not switched off within a usual time period. In addition, an old and damaged battery can develop a considerable amount of gas and become hot if it is charged at the power grid over a long period of time. The charging process at the power grid is usually performed without supervision and in an enclosed garage. This may lead to problems and thus also to customer dissatisfaction. Problems when charging lead acid batteries at the power grid are further aggravated by the fact that it is to be expected that batteries deteriorate as they get older.